Locking pedicle screw devices, methods, and systems

ABSTRACT

An embodiment of the invention provides for a pedicle screw system including a bone anchor, linkage rod, tulip, set screw, and detent plate. When the set screw is fully tightened against the detent plate, pluralities of ridges on opposing faces of the detent plate and set screw cooperate by providing catches to prevent unwanted loosening of the set screw, which could lead to unwanted rod slippage and instability in the orthopedic fixation unit.

This application is a continuation of U.S. patent application Ser. No.12/897,525, filed Oct. 4, 2010, the content of which is herebyincorporated by reference.

BACKGROUND

Spinal fixation devices can be used to provide, for example,immobilization and stabilization of spinal segments in patients (e.g.,humans, dogs, cats, and other animals). Fixation devices may be used tohelp fuse bone segments (e.g., vertebrae) in the treatment ofinstabilities or deformities of, for example, the cervical, thoracic,lumbar, and/or sacral spine. Such instabilities or deformities mayinclude, for example, degenerative disc disease (DDD);spondylolisthesis; trauma (i.e., fracture or dislocation); spinalstenosis; curvatures (i.e., scoliosis, kyphosis, and/or lordosis);tumor; pseudoarthrosis; and failed previous fusions.

However, there are risks associated with such fixation devices. Suchrisks include, for example, device component fracture, loss of fixationthrough connecting rod slippage, non-union, fracture of the vertebra,neurological injury, and vascular or visceral injury. For example,internal fixation appliances are load sharing devices used to obtainbone alignment until normal healing occurs. Thus, implants can breakand/or connecting rods can slip when fixation systems are subjected toloading associated with, for example, normal patient movements, delayedunion, or non-union situations. The degree or success of union, loadsproduced by weight bearing, and activity levels will, among otherconditions, dictate the longevity of the implant. Robust fixationsystems are needed to lessen risks associated with fixation and topromote better outcomes for patients.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of embodiments of the present invention willbecome apparent from the appended claims, the following detaileddescription of one or more example embodiments, and the correspondingfigures, in which:

FIG. 1 includes an assembly in an embodiment of the invention.

FIG. 2 includes a set screw, pivot, and detent plate in an embodiment ofthe invention.

FIGS. 3a and 3b include different perspectives of a detent plate in anembodiment of the invention.

FIG. 4 includes different perspectives of a detent plate in anembodiment of the invention.

FIG. 5 includes different perspectives of a set screw in an embodimentof the invention.

FIG. 6 includes different perspectives of a set screw in an embodimentof the invention.

FIG. 7 includes an assembly in an embodiment of the invention.

FIG. 8 includes a schematic flow chart for a method in an embodiment ofthe invention.

FIG. 9 includes an assembly in an embodiment of the invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. Well-known structures andtechniques have not been shown in detail to avoid obscuring anunderstanding of this description. References to “one embodiment”, “anembodiment”, “example embodiment”, “various embodiments” and the likeindicate the embodiment(s) so described may include particular features,structures, or characteristics, but not every embodiment necessarilyincludes the particular features, structures, or characteristics.Further, some embodiments may have some, all, or none of the featuresdescribed for other embodiments. Also, as used herein “first”, “second”,“third” describe a common object and indicate that different instancesof like objects are being referred to. Such adjectives are not intendedto imply the objects so described must be in a given sequence, eithertemporally, spatially, in ranking, or in any other manner. Also, theterms “coupled” and “connected,” along with their derivatives, may beused. In particular embodiments, “connected” may be used to indicatethat two or more elements are in direct physical contact with each otherand “coupled” may mean that two or more elements co-operate or interactwith each other, but they may or may not be in direct physical contact.

An embodiment of the invention provides for a pedicle screw systemincluding a bone anchor, linkage rod, tulip, set screw, and detentplate. When the set screw is fully tightened against the detent plate(thereby compressing the rod within the tulip), pluralities of ridges onopposing faces of the detent plate and set screw cooperate by abuttingeach other in a resistive manner to prevent unwanted loosening of theset screw, which could lead to unwanted rod slippage and instability inthe orthopedic fixation unit.

FIGS. 1-9 address various methods, embodiments, and perspectives oforthopedic linkage securing anchor assemblies.

In FIG. 1 anchor assembly 301 includes an anchor element 310 to attachto a bone. Element 310 may include a bone screw but is not so limitedand may include nails, pins, and the like. Assembly 301 further includestulip 305, which couples to anchor element 310. Tulip 305 includes openslot 302 to receive linkage 330. The linkage may include a rod forintervertebral fusion or fixation but is not so limited and may includewires, plates, and the like. Tulip 305 may include side walls defined byside wall edges 315, 316, 317, 318, which cooperate to define at least aportion of open slot 302. Assembly 301 further includes detent plate 335to couple to linkage 330 and reside, at least partially, between theside walls of tulip 305. In an embodiment detent plate 335 residesdirectly between respective opposing side wall edges 317, 318 and/or315, 316.

As seen in FIGS. 2-4, detent plate 335 has superior detent face 343including a radially disposed plurality of ridges. One particularrepresentative ridge is discussed for purposes of simplicity. To thatend, one such ridge includes resist face 337 formed at acute angle 338with respect to superior detent face plane 391. The ridge furtherincludes advance face 336 formed at acute angle 339 with respect tosuperior detent face plane 391. As used herein, an acute angle has ameasure of less than 90°. Angle 339 is “smaller” and “flatter” thanangle 338. In other words, the resist face is more steeply inclined thanthe advance face. The flatness of angle 339 and face 336 provides forrelatively easier advancement of set screw 350 across detent plate 335during initial set screw 350 tightening. The steepness of angle 338 andface 337 provides for relatively difficult loosening of set screw 350across detent plate 335 to help preclude or limit unwanted set screwloosening. In an embodiment, tip-to-tip distance 388 may be generally0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 mm and the likeand tip-to-trough distance 387 may be generally 0.5, 0.6, 0.7, 0.8, 0.9,1.0, 1.1, 1.2, 1.3, 1.4, 1.5 mm and the like. Also, in an embodimentadvance face 336 is flatter and bigger in total surface area than resistface 337 and advance face 356 is flatter and bigger in total surfacearea than resist face 357. This may be seen based on length 388 asopposed to the differential in lengths 387 and 388. The differential insurfaces areas is also readily seen in FIGS. 4 (top view of detentplate) and 6 (top view of set screw).

As seen in FIGS. 5 and 6, assembly 301 includes set screw 350 to closeopen slot 302, stabilize linkage 330, and fixedly couple to detent plate335 when rotated in tightening direction 392 (and decouple from detentplate 335 when rotated in loosening direction 393). Set screw 350 hasinferior set screw face 353 including a radially disposed plurality ofridges complimentary to the plurality of ridges included on detent plate335. One particular representative ridge is discussed for purposes ofsimplicity. To that end, one such ridge on set screw face 353 includesresist face 357 formed at acute angle 394, with respect to inferior setscrew face plane 396, and advance face 356 formed at acute angle 395,with respect to inferior set screw face plane 396, which is smaller andflatter than angle 394.

Thus, when set screw 350 is forced in tightening direction 392 incertain situations such as, for example, while set screw inferior face353 initially contacts detent plate superior face 343, the ridges of setscrew 350 advance in tightening direction 392 skipping intermittentlyacross, with limited resistance, the ridges of detent plate 335.

Also, consider the situation where, for example, set screw inferior face353 is already in contact with detent plate superior face 343 after fulldeployment in a patient and with set screw 350 being fully tightenedagainst detent plate 335. In that situation, when set screw inferiorface 353 is forced in loosening direction 393 the resist faces 337, 357are mated and the ridges on set screw 350 are halted to preventloosening of set screw 350 and consequent destabilization of linkage330. The phrase “forced in loosening direction” generally means a forceis applied in the loosening direction. The phrase does not necessarilysay any resultant motion or rotation occurs. Also, such forces may occurfrom general movements made by the patient, by the surgeon, and thelike.

In other words, detent plate 335 may be used to mechanically resist orarrest the rotation of a wheel, axle, or spindle such as ridged inferiorset screw face 353. The ridges of detent face 343 can be used tointentionally divide rotation of set screw 350 into discrete incrementsand/or to simply arrest rotation of set screw 350 in a looseningdirection 393. The resist faces 337, 357 operate to resist loosening ofset screw 350 once the set screw is tightened to detent plate 335. Theuse of “advance” faces 336, 356 helps set screw 350 “advance” whiletightening to detent plate 335. Thus, in one embodiment the advancefaces are angled so that the wheel of ridges on set screw 350 rotateseasily in direction 392, as tip 397 easily lifts or is pushed out oftrough 398. Following this, tip 397 advances into the next notch on thedetent plate as the ridged wheel of set screw 350 continues rotating.Angles 339, 395 may range in different embodiments to include 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60 degrees and so on. For example,angles 339, 395 may each be less than 15 degrees. As another example,angles 339, 395 may each be 5 degrees or less.

In contrast, angles 338, 394 are more severe (i.e., less flat) and mayrange in different embodiments to include 15, 20, 25, 30, 35, 40, 45,50, 55, 60, 65, 70, 75, 80, 85, and 90 degrees so tip 397 cannot beeasily pushed up or out of trough 398 if the ridged wheel of set screw350 is forced (although not necessarily moved) in the looseningdirection 393. For example, angles 338, 394 may each be more than 15degrees. As another example, angles 338, 394 may each be 30 degrees ormore.

As used herein, an orthopedic set screw is a type of orthopedic screwgenerally used to secure a fixation linkage within a holder. The setscrew may be fully threaded and may or may not have an external head.Set screw 350 may be inserted into tulip 305 using any number of driverssuch as an internal Hex, Allen, slot, Torx, star or Phillips key ordriver. Orthopedic set screws may pass through a threaded hole in anouter object, such as a tulip, and be tightened against an inner object,such as an intervertebral fixation rod, to prevent the inner object frommoving relative to the outer object. The orthopedic set screw exertscompressional or clamping force through the bottom tip of the set screw.

In an embodiment, detent plate 335 includes inferior detent face 344including concave portion 338 contoured to complement an outer profileof linkage 330. Such an outer profile may be spherical but otherprofiles (e.g., elliptical, square, flat, oval) are possible.

In an embodiment detent plate 335 and its ridges, used to couple toridges on set screw 350, are monolithic. In other words, the ridges offace 343 may be formed to plate 335 without seams and formed from asingle material. In other embodiments there may be intervening plates orother materials between plate 335 and ridges 336, 337. Also, in anembodiment set screw 350 and the ridges on face 353 are monolithic. Inother embodiments there may be intervening plates or other materialsbetween set screw 350 and ridges 357, 356.

As seen in FIG. 9, in an embodiment detent plate 335 is permanentlycoupled to set screw 350 via pivot member 340 so detent plate 335 canpivot about (see arrows 377, 378) set screw 350 when the set screw isnot fully tightened against the detent plate. This rotation is possiblebecause space 379 exists between plate 335 and screw 350 when the twoare not fully tightened against one another (yet still loosely coupledto one another via pivot 340). However, when the two are fully tightenedagainst one another space 379 is removed as face 343 fully mates to face353. By permanently coupled, a person of ordinary skill in the art willappreciate that using extraordinary means the detent plate and set screwcan be separated. However, a “permanently coupled” embodiment in typicalclinical situations may allow a surgeon to avoid having to individuallyplace the detent plate and set screw into the tulip. Instead, he or shemay place the detent plate and set screw into the tulip as a permanentlycoupled unit. This facilitates ease of handling in the surgicalenvironment. Also, the pivot member allows for orienting the detentplate as needed to couple to the linkage and also allows the set screwto then tightly couple to the detent plate.

In an embodiment set screw inferior face includes maximum breadth 382less than maximum breadth 381 of detent plate superior face. In anembodiment, detent plate maximum breadth 381 may be generally 9.5, 9.6,9.7, 9.8, 9.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 mm and the like and minimumbreadth 386 may be generally 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7,5.8, 5.9, 6.0 mm and the like. In an embodiment, after set screw 350 isfully tightened against detent plate 335, and the set screw is forced inloosening direction 393 (but not necessarily moved in direction 393),side face 342 of detent plate 335 abuts one of the tulip side wallsdefined by wall edges 315, 316, 317, 318 to halt rotation of detentplate 335 and prevent loosening of set screw 350 and destabilization oflinkage 330.

In an embodiment, set screw threads 352 mate with corresponding threads383 included in walls of tulip 305. In an embodiment, when set screw 350is fully tightened against detent plate 335 and the set screw is forcedin loosening direction 393, rotational movement of linkage 330, aboutlongitudinal axis 384 of anchor element 310, is halted by a side wall oftulip 305 and translational movement of linkage 330 along horizontalaxis 385, perpendicular to longitudinal axis 384, is halted by detentplate 335.

Thus, some embodiments provide that when a set screw is fully tightenedagainst a detent plate, pluralities of ridges on opposing faces of thedetent plate and set screw cooperate by providing catches to preventloosening of the set screw until a loosening force surpassing a firstthreshold is applied to the set screw. That is to say, in an embodimentthe detent plate is not irreversible. Once the set screw is fullytightened to the detent plate, the set screw can be loosened. However,the detent plate makes such loosening more difficult and less likely toinadvertently occur during, for example, typical movements by thepatient once the implant has been installed.

FIG. 7 includes an assembly in an embodiment of the invention. Assembly401 includes no detent plate or pivot member such as shown in FIG. 1.Instead, linkage 430 may include longitudinal ridges. Taking one suchridge as an example, the ridge includes resist face 437 and advance face436. Principles of operation for assembly 401 resemble those forassembly 301. However, set screw 450 mates directly to linkage 430. Setscrew 350 (FIG. 5) may be substituted for set screw 450. Thus, duringtightening advance faces 436, 356 may cooperate to allow tighteningwithout a great deal of rotational force. However, resist faces 357, 437may cooperate to resist, entirely or substantially, loosening of setscrew 450 within tulip 405, thereby stabilizing linkage 430. The outerprofile for linkage 430 may be spherical but other profiles (e.g.,elliptical, flat, square, oval) are possible.

Embodiments of methods for employing devices described herein are nowaddressed. In FIG. 8, method 800 includes block 805 where sitepreparation occurs. Specifically, after exposing pedicle screw entrypoints, a starting hole may be started with a burr, rongeur or bone awl.The awl may insert to a depth of 20 millimeters. Fluoroscopy may beutilized by the surgeon to allow for more accurate placement of pediclescrews. Alternatively, plain x-ray may be utilized to visualize theappropriate trajectory. The surgeon may enter the pedicle with thepedicle probe. The angled or straight probe may be utilized at thesurgeon's discretion. A smaller diameter probe may be made available forsmaller or more difficult pedicles. The probe should be rotated withentry to allow for the path of least resistance and to reduce stress onthe probe. Calibration on the shaft is utilized to choose theappropriate length screw. Depth should be measured from the initialentry point. A ball tipped probe may then be placed in the pedicle holeto aid in checking for intact walls and determining if the anteriorcortex is intact at full depth. Depending on bone density at theinsertion site, a tap may be utilized to ease the insertion of thescrew.

In block 810, screw selection is made. Screw diameter options mayinclude 4.5, 5.5, 6.5, 7.5, 8.5 mm and the like. All screw diameters maybe available in a tray. The screw may then be placed on the driver, heldsecurely by interference fit, and through a tulip. The driver may beratcheted for clockwise or counter clockwise rotation or fixed position.The screw and tulip may then be inserted until the bottom of the screwhead is flush with the bony cortex. Alternatively, the screw may beallowed to seat slightly higher to aid in alignment for rod placement ifthe surgeon chooses. The driver may disengage by simply pulling itdirectly out of the screw hex receiving point. Rod selection may then bemade. Both pre-bent and straight rods may be available. Rod lengths mayinclude, for example, 35 mm, 40 mm and so on with 10 mm increments upto, for example, 150 mm in a standard set.

In block 815, the screw head may remain in position after adjustment.The screw heads and tulips may be aligned with a tulip positioner toallow for easy rod placement. Screw heads and tulips may be angled toallow for easier rod placement and for future screw removal ifnecessary.

In block 820, the rod may be clamped by a rod holder and seated into thescrew heads. If necessary, the assembly may come with a reduction screwoption that includes a tulip with extended tabs or side walls tofacilitate access (e.g., move tissue aside) to the inside of the tulipnear the anchor or screw head. These extended tabs should allow for easycapture of the rods if the surgeon so chooses. The extended tabs may beconfigured to “breakaway” when the surgeon has completed deviceinsertion and wishes to minimize the profile of the hardware to remainin the patient.

In block 825, a set screw and detent plate, such as the embodimentsdescribed herein in conjunction with FIGS. 1-7 and 9, may be insertedinto the tulip. The set screw and detent plate may be insertedseparately into the tulip. However, the set screw and detent plate mayalready be coupled via a pivot member and the entire set screw—pivotmember—detent plate combination may be placed in the tulip at one time.The set screw may be rotated counterclockwise initially to allow forseating within the threads of the tulip. The set screw may then beadvanced down to the rod by rotating the set screw clockwise. When theset screw and detent plate are provisionally seated, the rod placementwithin the screws can be adjusted prior to final seating. Once seated,before final tightening, the rod may be lightly held in position to aidin the prevention of further rod movement.

In block 830, the set screw and detent plate may be fully tightened tothe rod using an anti-torque device which is seated on the rod. Theinsertion driver may continue to rotate, and the screw may advance a bitmore as the ridges on the set screw advance over the complementaryridges on the detent plate. This may occur until the set screw is fullytightened to the detent plate. A torque driver may be used that has abreakaway feature which occurs at, for example, 12 N-m of torque. Thescrew may be advanced until a click is heard which indicates the“breakaway” occurred. The set screw and detent plate may then be fullyseated.

Embodiments herein have focused on spine fixation systems butembodiments are not so limited and may have utility in more generalorthopedic fixation systems used in, for example, fixation of fracturedlong bones, limbs, and the like.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

What is claimed is:
 1. An orthopedic system comprising: a tulip, tocouple to an anchor, which includes a slot to receive a linkage; adetent plate, to couple to the linkage, with a detent face includingfirst ridges; a set screw with a set screw face including second ridgescomplimentary to the first ridges; wherein (a) when the set screw face,with the set screw partially tightened and initially contacting thedetent face, is forced in a tightening direction the second ridges arenot stopped by the first ridges; (b) when the set screw face, with theset screw fully tightened, is forced in a loosening direction the secondridges are stopped by the first ridges to prevent set screw looseninguntil a loosening force surpassing a first threshold is applied to theset screw; (c) the detent plate is fixedly coupled to the set screw, (d)a first space exists between the first and second ridges when the setscrew is not fully tightened and the first space is removed when the setscrew is fully tightened, (e) a coupler directly connects to the setscrew and the detent plate; (f) each of the first ridges includes afirst resist face formed at a first acute angle of at least 30 degreeswith respect to the detent face and a first advance face formed at anadditional first acute angle of no more than 5 degrees with respect tothe detent face; (g) each of the second ridges includes a second resistface formed at a second acute angle of at least 30 degrees with respectto the set screw face and a second advance face formed at an additionalsecond acute angle of no more than 5 degrees with respect to the setscrew face; (h) the first acute angle is equal to the second acute angleand the additional first acute angle is equal to the additional secondacute angle, and (i) a magnitude of the first threshold is based on thefirst acute angle, the additional first acute angle, the second acuteangle, and the additional second acute angle.
 2. The system of claim 1,wherein the detent plate includes a concave portion complementary to anouter profile of the linkage.
 3. The system of claim 2, wherein thedetent plate, the detent face, and the first ridges are monolithic witheach other and the set screw, the set screw face, and the second ridgesare monolithic with each other.
 4. The system of claim 3, wherein theset screw includes threads complimentary to threads included in a sidewall of the tulip.
 5. The system of claim 4 wherein the linkage includesan intervertebral fixation rod and the anchor includes a bone screw. 6.The system of claim 5, wherein the detent plate is fixedly coupled tothe set screw via the coupler so when the detent plate, coupler, and setscrew are removed from the tulip the detent plate, coupler, and setscrew are still coupled to one another.
 7. The system of claim 6,wherein the first and second ridges are both radial.
 8. The system ofclaim 7, wherein the coupler directly connects to the set screw and thedetent plate so the detent plate rotates about the set screw whileremaining fixedly coupled to the set screw.
 9. The system of claim 1,wherein the first acute angle and the additional first acute angle areinterior angles for a triangle defined by the detent face, the firstresist face, and the first advance face.
 10. The system of claim 9,wherein the second ridges mate flush with the first ridges when thefirst space is removed and the set screw is fully tightened.
 11. Thesystem of claim 1, wherein the detent plate is permanently coupled, andnot removably coupled, to the set screw via the coupler.
 12. The systemof claim 1, wherein the detent face outer profile is non-circular. 13.The system of claim 1, wherein when the set screw is fully tightened andforced in the loosening direction, a side face of the detent platepasses completely through an outermost edge of a channel that completelytraverses the tulip.